Telephone system



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' TELEPHONE SYSTEM FiledJuly 26, 1941 10' Sheets-Sheet 10 ccrIllllllllll A TYTORIVEVI Patented Nov. 3, 1942 UNITED STATE iATE OFFlCETELEPHONE SYSTEM Application July 26,1941, Serial No. 404,109

9 Claims.

This invention relates to telephone systems and particularly to smallcapacity telephone systems in which crossbar switches are employed. Anobject of the invention is to provide means whereby line stationsequipped with different types of call devices may operate commonapparatus with which to set up desired connections as, for instance,between a station equipped with a dial sender to transmit a series ofimpulses designating a called number and a station that utilizes analternating current generating device to generate and transmitcombinations of different frequencies to designate the called linenumber.

, Heretofore, systems have been provided for establishing connectionsbetween two subscribers lines in single crossbar units wherein all ofthe calling stations were equipped with dial sending devices as, forinstance, the system disclosed in Patent No. 2,071,075 issued to CharlesD. Koechling on February 15, 1937.

A feature of the present invention is an arrangement in a system of theabove kind in which a connection may be established between twosubscriberslines by means of a link which, on the one hand, is adaptedto respond to dial pulses produced at an originating station equippedwith a dial to set up a connection to the station indicated by thepulses and, on the other, is also adapted to respond to combinations ofcurrents of-diilerent frequencies generated at an originating station,to set up the connection to the station indicated by such combinationsof frequencies. The link is provided with suitable registers forresponse to either type of pulses,

the direct current register, however, being the one which, in all cases,operates the hold magnet of the called line in the crossbar switch. Atranslator is provided whereby, in response to the settmg of thereglster that respfinds to the albeen given a numerical designation 2!)while line ternating current pulses designating the digits of the calledline, the direct current register is set for those which then controlsmeans for operating the hold magnet of the called line.

The invention is illustrated in connection with the following drawingsin which:

Figs. 1 and 2 show, diagrammatically, a crossbar switch frame of knownconstruction having ten horizontal outlets and twenty verticals to eachof which a subscribers station is connected.

The first vertical, assigned to station A, has a line number designation2t, and the last vertical, assigned to station B, has a numberdesignation 39, station A being provided with a dialing device LD andstation B being provided with an alternating current or key pulsinggenerating device LG;

Fig. 3 in the left portion thereof, shows a link allotter circuit, whilethe rest of this figure, together with Fig. 4 show the call allottercircuit;

Figs. 5, 6, 7, 8 and 9 show the details of the link circuit;

Fig. 10 shows, in diagrammatic form, two other links and a powergenerating, tone and alarm circuit; while Fig. 11 shows the manner inwhich Figs. 1 to 10, inclusive, should be arranged with respect to eachother to completely disclose the invention.

The invention will now be described in cletail by describing theoperations necessary to set up two different types of connections;namely, a connection originating at station A for station 13, in whichthe number designation 39 of station B will be dialed at station Athrough the manipulation of dialing device LD thereat, and a connectionoriginating at station B for station A in which the number designation2%) of station A will be set up on device LG by the depression thereonof keys (not shown) corresponding to the digits of the designatedstation.

Before describing the detailed operation of the invention, however, itis desirable to call attention to the fact that the illustrativeembodiment of the invention is being shown in connection with a smalloffice having a maximum capacity of twenty lines, each station of whichis equipped with either a dial ID or a generator LG for transmittingcalled line designations. Each line appears on one of the twentyverticals of the crossbar switch, conventionally shown in Figs. 1 and 2,and each, for simplicity, has been given a numerical designationcorresponding to the vertical to which it is connected. Thus line A isconnected to vertical 20 and, therefore, has

B which is connected to vertical 39 has been given a numericaldesignation of 39, the intermediate eighteen lines (each of which isprovided either with a dial LB or a generator LG) being given numericaldesignations corresponding to the different verticals of the frame towhich they are severally connected.

The dial LD is the ordinary impulse dial well known in automatictelephony and its manipulation interrupts the line to produce a seriesof pulses the number of which corresponds to the digit to which the dialis pulled over to the stop attachment prior to releasing it for itsreturn to normal in the course of which the train or series of impulsesis produced. The device LD, on the other hand, is an alternating currentgenerator which, for example, may be of the type shown in Patent No.2,147,710 granted to R. F. Mallina on February 21, 1939. It comprises anumber of reeds which may be plucked in pairs to produce vibrationswithin a magnetic field and thereby cause the generation of currentshaving frequencies determined by their several physical constants. Thesecurrents are transmitted over the link into registers therein for use incausing the link to complete the connection to the desired line.

For the quantity of internal traffic which may arise within the twentylines of the system only three links are provided each of which occupiestwo horizontal outlets of the crossbar switch, link I (the circuit ofwhich is shown'in detail in Figs. to 9, inclusive) occupying the twouppermost outlets controlled, for selective purposes, by select magnets8 and 9; link 2 occupying the two horizontal outlets immediately belowthose of link I and controlled by select magnets 6 and I, while link 3occupies the two horizontal outlets immediately below those of link 2and controlled by select magnets 4 and 5. The remaining four outlets ofthe switch may, if desired, be used as outgoing trunks or links.However, since the invention is not concerned with outgoing connections,these outlets are not shown connected either to links or trunks.

Referring, now, to Fig. 3, there are shown three relays, namely, relaysCHI, CH2 and CH3, which form a link allotter circuit, the first tworelays being shown in an operated position while the last is shown in anunoperated position.

These three relays control the sequential allotment of an available linkto a calling line and the function of the first two relays in theposition shown is to route the start conductor I to the first idle linkavailable to the ofiice. As said before, in the present embodiment ofthe invention it is assumed that the trafiic between the various linesof the oifice may be properly satisfied by the use of but three links sothat the relays CHI, CH2 and CH3 serve to route a calling line to one ofsaid three links depending upon which one of them is free in the orderof allotment. The operated condition of relay CHI indicates that thelink to which it provides access is in an idle condition, its lockingcircuit (that is, the locking circuit of relay CHI) extending frombattery through the winding thereof, contacts of KYI, conductor 2, No. 1contacts of relay B of link I, conductor 3, No. 3 front contacts ofrelay CHI to ground. The locking circuit of relay CH2 which controlsaccess to the second link is traced over a path which extends frombattery through its winding, key KY2, conductor 2 in the bracket line 4,through the No. 1 back contacts of relay B in link No. 2(diagrammatically indicated in Fig. conductor '3 in the bracket line 4,No. 5 contacts of relay CH2 to ground.

On the other hand, the operating circuit of relay CH3 which providesaccess to link No. 3, while traceable over its associated key KY3,conductor 2" within bracket line 5, through the No. 1 contact of relay Bin link 3 (diagrammatically shown in Fig. 10) and conductor 3" withinbracket line 5, terminates in the No. 3 normal contacts of relay CH3 andalso in the No. 3 open contacts of relay CHI.

In other words, a calling line, to have accessibility to link I, relaysCHI and CH2 must be operated while relay CH3 must be normal.

It will be shown that as each link is allotted in rotation, the circuitsof relays CHI, CH2 and CH3 are changed to provide for the advance ofstart conductor I from one link to the next in the order named.

Bearing in mind the condition of relays CHI, CH2 and CH3 of the allottercircuit as described above, it may now be assumed that a call isoriginated at station A for station E by the removal, at the formerstation, of the telephone instrument from its cradle, whereupon acircuit is completed for relay L29 of said line which extends frombattery over the upper normal contacts of the hold magnet HOZiiassociated with vertical 29, winding of relay L20, ring conductor R,over the station loop, tip conductor T, No. 1 normally made contacts ofrelay L28 to ground on the No. 1 contacts of cut-ofi relay C026. RelayL29 operates. Over its No. 1 contacts, the ground terminal of itscircuit is switched from solid ground on the No. 1 contacts of relay COto ground through the secondary Winding of transformer LBT to theprimary of which a source of distinctive tone is connected fortransmission to the calling line in the event that no link is availablefor completing the connection, as will be described shortly.

Over its No. 2 and No. 3 contacts, relay L20 causes a circuit to becompleted for relay LI of the call allotter circuit (there being one LIrelay for each line) and relay ST of link I which, since relays CHI andCH2 of the allotter are assumed to be locked and relay CH3 is assumed tobe normal, is the preferred link in the order of selection. The circuitfor the relays ST and LI is traced as follows: Ground through the No. 1contacts of relay EI, winding of relay LI, conductor 6, No. 2 and No. 3contacts of relay L20, start conductor I, No. 3 contacts of relay CH2,No. 1 contacts of relay CHI, conductor 1, winding of relay ST tobattery. Both relays LI and ST operate in this circuit. Relay LI, uponoperating, opens the locking circuit of all other nineteen LI relays atits No. 4 contacts and completes a circuit for relay N, which circuitmay be traced from ground on the No. 1 contacts of relay LI, conductorIll, No. 1 back contacts of relay M, No. 4 contacts of relay MS, windingof relay N to ground. Relay N operates and completes a circuit for relayM from ground on its No. 2 contacts, No. 1 back contacts of relay MS,winding of relay M to battery. Relay M operates and opens the circuit ofrelay N at its No. 1 back contact causing it to release while therelease of relay N opens the circuit of relay M which, however, remainslocked under the control of the No. 1 contacts of relay MS and its ownNo. 2 contacts to ground on conductor IE1. When relay MS operates asdescribed below, relay M releases. This cycle for operating relays M andN ordinarily performs no useful function but will perform an emergencyfunction that will be explained in its proper sequence. At the sametime, relay LI completes another circuit for relay E which may be tracedfrom ground on the No. 1 contacts of relay EI, No. 2 contacts of relayL, conductor 3, serially through the No. 1 back contacts of theindividual link relays LKS, LKZ and LKI, conductor 9, winding of relay Eto battery. Relay E upon operating, locks to ground on the No. 1contacts of relay LI and at the same time closes a circuit for relays EIand E2 from ground on its contacts, No. 2 normally made contacts ofrelay MS to the windings of relays EI and E2 to the other respectiveterminals of which battery is connected. Relays EI and E2 operate butrelay LI, which operated from ground on the No. 1 contacts of relay El,now holds locked on battery through relay SI of the selected link aspreviously traced to conductor B, winding of relay LI and its No. 2contacts, conductor 8 as traced to conductor 9, contacts of relay E toground on the No. 1 contacts of relay LI. Hence with the operation andlooking of relay LI individual to station A, and with the operation ofrelays EI and E2, all other lines may not receive service if calls areinitiated thereat while station A is in the process of having a linkassigned since, with relays El and E2 operated, no ground is availablefor completing the circuit of the relays LI of the respective callinglines.

When relay EI operates, it completes a circuit for relay MS, saidcircuit tracing from ground on conductor It, No. 14 contacts of relayEI, winding of relay MS to battery. Relay MS operates after an interval,opens the path of relay N, supplies holding ground over its No. 2contacts for relays El and E2 and applies ground on conductor It! toconductor II over its No. 3 contacts. Ground on conductor II is used tocomplete the circuit of the link select magnet 9 in virtue of operationswhich have been taking place in the link as a result of the operation ofrelay ST therein and which will shortly be described.

In the event that, due to some trouble condition, relay E of the callallotter fails to operate, relay MS cannot operate and ground will notbe applied to conductor I I over its No. 3 contacts. Under thesecircumstances it is desirable to complete the connection if possible andso emergency means are provided for applying ground to conductor I! inthe event that relay MS fails to operate. It will be remembered thatupon the operation of relay LI a circuit was completed for relay N, andthat prior to the operation of relay MS/relay N caused the operation ofrelay M. Now, when relay lVl" operates, it opens the circuit of relay Nbut relay M remains looked over its No. 2 contacts to ground onconductor Ill, and it will be observed that, with relay N normal andrelay M operated, ground on conductor I0 is applied to conductor I 1 viathe No. 1 front contacts of relay M and No. 1 contacts of relay N.

Returning, now, to the operation of relay ST, a circuit is completed forselect magnet 9, which circuit traces from battery through the windingof said magnet, conductor H, No. 2 contacts of relay B, N o. 4 contactsof relay ST, conductor I I, to the aforetraced ground thereon. Selectmagnet operates and preselects the group of cross,- points on itshorizontal level, including crosspoint I through which the calling loopis extended into the link as shown hereinafter. Magnet 9, uponoperating, completes a circuit from ground, over its contacts and commonconductor I3 to the windings of relays S and Si in parallel causing saidrelays to operate and complete a circuit for cut-oif relay C029, saidcircuit tracing from ground on the No. 3 contacts of said relays, No. 3contacts of relay Ll, conductor I9, winding of relay C025 to battery.Relay COZil upon operating, closes an obvious circuit for hold magnetHOZiI of the Vertical 29 to which line A is conwhich links I and 2- areunava' nected and, in so doing, operates crosspoint I. This crosspointremains operated after the circuit of select magnet 9 has been opened,is standard crossbar switch operation and need not be amplified anyfurther. When hold magnet H028 which may be traced operates, it releasesline relay L20 in turn releasing relay LI and those relays controlledthereby. Relay L20 further disconnects ground from start conductor Iwhich caused the operation of relay ST. However, since crosspoint I isclosed, this relay will not release, having a locking circuit through acrosspoint contact, which may be traced over the No. 2 contacts of saidrelay, No. 1 contacts of relay T2, conductor SI, No. 3 contacts ofcrosspoint I, to ground.

Since line crosspoint I is operated, the line tip and ring conductors Tand R are joined to the link tip and ring conductors LT and LR,respectively, over the No. 6 and No.5 contacts of the operatedcrosspoint I, respectively, and this connection completes an operatingpath for relay .A from battery through its lower Winding, No. 2 backcontacts of relay HS, conductor LT, contact 6 of crosspoint I, lineconductor T, over the loop, ring conductor contact 5 of crosspcint I,conductor LR of the link, No. 3 back contact of relay HS, upper windingof relay A, to ground. Relay A, u on operating, completes a circuit forrelay B, which circuit extends from ground on conductor SI, front con:tacts of relay A, No. 4 normally made contacts of relay B, winding ofrelay B to battery, causing said relay to operate and lock over its No.4 front contacts to ground on conductor Si. Rela B, at its No. 2contacts, opens conductor ll thereby causing the release of the selectmagnet s. Since however, the hold magnet H023 is operated, crosspoint Iremains operated. Relay ]3 further completes a circuit from ground overitsNo. 3

contacts to a relay (not shown) in the power charge circuit Hill tooperate circuits thereby that will increase the charging rate to thelink power supply while the link is being used and, over its No. 5 andN0. 6 contacts, connects ground to holding conductors 20 and 2! forholding andopcrating certain other relays as described hereinafter. Overits No, 1 contacts it opens the looking circuit of relay CHI in theailotter circuit which, upon releasing, advances the common startconductor I over the Nlo. 3 contacts of relay CH2, No. 2 contacts ofrelay CHE. No. 1 contacts of relay CH2 to conductor 1' which further ex}tends to relay ST of link 2.

It is now evident that if. at the time the call was initiated at stationA, link I was busy or was otherwise unavailable, its relay CHI in thelink allotter circuit would have been normal, and the start wire I, withground applied thereto, would have been connected to conductor 7' oflink 2 to cause the operation therein of relay ST in the same manner asthat of relay ST in link I as already described. On the other hand. ifboth links I and 2 were busy or otherwise unavailable, relay CH2 as wellas relay CH! would have normal since their respective locking circuitswould be opened at the No.1 contacts of relay B of their respectivelinks. However. as soon these relays are both normal. a circuit iscompleted for relay CH3 which extends from battery through its winding.conductor 2". No. 1 contacts of relay B of link 3, conductor 3%". toover the No. 1 normally mad contacts of relay CHI. RelayCHil operatesand, with relays CH6 and CH2 normal, represents the condition in do butlink 3 is available. Now if a call is l tied at a line station forinstance, station A, ground on start conductor I is extended conductorl" which is connected to the winding of relay SI of link 3, the pathbeing from ground on conductor I, No. 4 contacts of relay CH2, No. 2contacts of relay CH3, conductor 7', to the winding of relay ST of saidlink causing its operation and the connection of the link to the callingline.

If all three links are unavailable, relay CH3 will be normal along withrelays CHI and CH2. The initiation of a call under these circumstanceswill cause ground on the start conductor I to be applied to conductor 22via the No. 4 contacts of relay CH2, No. 1 contacts of relay CH3, No. 2contacts of relay CHI, No.'2 contacts of relay CH2, to conductor 22.This conductor extends (through bracket line I3) to the power, tone andalarm circuit lit] and closes a circuit therein which causes a distinctlink busy tone to be applied to the conductors 23 and 2% connecting withthe primary winding of busy tone transformer LBT. Since the secondarywinding of this transformer is connected to ground and is completed intoa circuit over the line loop to battery on the upper normally madecontacts of the hold magnet HO- through the winding of relay L-, thesubscriber at the calling station will hear the tone as an indicationthat, due to unavailable links, the connection cannot be established.

As soon as a link becomes available, say link I, then a circuit iscompleted for relay CHI which extends from battery through its winding,thence as traced to conductor 3, No. 5 contacts of relay CH2 to ground.Relay CHI operates and locks to ground over its No. 3 contacts toreestablish the path of start conductor I'to the winding of relay ST inreadiness for seizure on the next call. If link 2 becomes available,relay CH2 operates over a circuit traceable from battery through itswinding, thence as traced to conductor 3' to ground on the No. 3normally made contacts of relay CH3.

Returning, now, to the operation of relay ST of link I assumed to havebeen taken into use, ground on the No. 3 contacts of said relaycompletes a circuit for relay LSI of its private link connector and thiscircuit is traced from ground on said contacts, conductor 58, winding ofrelay LSI. serially through the No. 2 normally made continuity contactsof relays LS2 and LS3 (the former being individual to link 2 and thelatter individual to link 3) to battery. Relay LSI operates. connectsoperatingbattery to its winding through its own No. 2 front contactsand, over its No. 1 front contacts, completes an obvious circuit forcut-in relay LCI which operates as a result thereof.

The object of operating relays LSI and LCI is to connect the commonalternating current pulse receiver and translator shown in Figs. 8 and 9to the link taken into use, and when this circuit is s connected. the sinal for which is the operation o relay LSI, said receiver must be madeunava lable to other l nks. This is done by removin the ope a in roundfor relays LC2 and 03 at the No. 1 back contacts of relay LSI so that,if either relay LS2 or LS3 should have its operatin circuit establ shedby relay ST of its respective link. the circuit of relay LC2 or LC3 iscut off at the No. 1 back contacts of relay LS5. On the other hand. ifthe first calling link happens to be li k. 2 or 3. then. hecorresponding operation of relays LS2 or LS3 will ut off the operatingcircuit of relay LSI at their respective No. 2 normal- 1v madecontinuity contacts so that if link I is seized in the meanwhile. thefailure of relay LSI to operate will prevent the operation of relay LCIand thereby prevent the simultaneous connection of the commonalternating current receiver and translator to two calling links. Thealternating current receiver of Fig. 9 is adapted to receive alternatingcurrent impulses from a calling station equipped with an alternatingcurrent generating device such as, for example, the device LG at stationB. At the time a call is initiated, however, the seized link has noknowledge of which type of station is making the call. Hence it must beprepared, at first, to receive either direct current pulses from a dialID or alternating current pulses from a generating device LG. Since thelink itself is normally arranged with a register to receive directcurrent pulses, as will be shown shortly, the alternating currentreceiver common to all links must be connected to a calling link beforethe calling subscriber can be advised, by an appropriate warning tone,to transmit the called line designation. Accordingly, when relay LCIoperates, a circuit is completed for relay GR which extends from groundon conductor M, No. 1 back contacts of relay C, conductor 75, No. 4contacts of relay LC I, conductor I8, winding of relay GR to battery.Relay GR operates and disconnects ground from conductors II and 12which, as will be shown, are connected to the calling loop through theoperation of relay ON. A circuit is also completed for relay ON which istraced from ground on the N0. 5 contacts of relay LCI, conductor 69,winding of relay ON to battery. Relay ON operates and, over its No. 1contacts, closes through a low frequency tone circuit derived from thetone oscillator It through adjustable resistance pad 62 and transformer6|. The path is traced as follows: From the lower terminal of thesecondary winding of transformer 6|, conductor I l, No. l contacts ofrelay ST, conductor I5, No. 6 contacts of relay LCI, conductor I5, No. 3contacts of relay RR, No. 2 contacts of relay RA, No. 1 contacts ofrelay ON, conductor I2, through the low-pass filter 63 to the upperterminal of the secondary winding of transformer 6|. The tonefrequencies produced by the oscillator 'Iil are thus induced over thesecondary circuit above traced.

Through a transformer arrangement in the low-pass filter E3, the lowfrequencies are induced in the closed circuit comprising the transformer68, a transformer in said low-pass filter and a transformer in high-passfilter fi l. Beyond the secondary winding of the transformer in thefilter 64 are connected suitable filter networks which are designed topass only frequencies Within the signal frequency band of thefrequencies that are produced by the. station generator LG whenoperated. Hence the tone frequencies produced by oscillator it will notpass into the volume limiter or into the enabler 89. They will, however,be induced into the secondary winding of transformer 53 if saidsecondary winding is closed into an electrical system, which it isbecause conductors II and I2 are but extensions of the line conductors Tand R into the link and alternating current receiver connected thereto.The path is traced as follows: From the left side of the secondarywinding of transformer 63, conductor H, No. 2 contacts of relay ON,conductor 53, No. 7 front contacts of relay LCI, conductor 54, condenserC2, No. 2 back contacts of relay HS, conductor LT, No. 6 contacts ofcrosspoint I, conductor T, over the loop of station A, conductor R, No.5 contacts of crosspoint I, conductor LR, No. 3 back contacts of relayHS, condenser C3, conductor 55, No. 8 front contacts of LCI, conductorI4, No. 5 contacts of relay ON, conductor 72 to the right terminal ofthe secondary winding of transformer 68. Inasmuch as the receiver of thetelephone instrument of station A is included in the above closedcircuit, the tone induced thereover is heard by the subscriber, which heunderstands as a signal to proceed with dialing the number of the wantedsubscriber.

The subscriber, upon receiving a tone, operates the dial ID to transmitthe called line designation. In the present embodiment of the invention,it is assumed, as said before, that the capacity of the ofiice is twentylines and that the number of designations of said line extends fromtwenty to thirty-nine, inclusive, it being further assumed that stationA has a designation of 29 and that station B has a designation of 39.The calling subscriber, therefore, dials a wanted designation by dialingtwo digits, the first of which may be a 2 or a 3 and the second of whichmay be any digit from to 9. Since the connection is to be establishedbetween the calling line A and called line B, the subscriber at A willfirst manipulate his dial to transmit three pulses for the tens digitand, thereafter, nine pulses for the units digit.

As is well known, the operation of the dial LD makes and breaks thecalling line loop as many times as required to produce the pulsesrequired for the digit. Hence upon dialing the digit three, three pulsesare produced that will cause three successive releases of relay A. Whenrelay A releases on the first pulse, it completes a circuit for relay Plwhich extends from ground on conductor Sl, the back contacts of relay A,No. 3 contacts of relay B, No. 2 contacts of relay E, back contacts ofrelay P2, No. 2 back contacts of relay P3, winding of relay Pl tobattery. Through the No. 1 back contacts of relay P3, a branch circuitfurther extends to the winding of slowrelease relay C. Both relays P!and C operate and short-circuit the lower winding of relay P2, ground toone side of this winding being supplied over the No. 2 contacts of relayC while ground on the other side of the winding is supplied over the No.1 contacts of relay P1 to the back confacts of relay A. With theoperation of relay Pl a circuit is completed for relay SW which extendsfrom battery through its upper winding and No. 2 normally made contacts,No. 5 back contacts of relay T2, No. 2 front contacts of relay Pi,conductor 23, No. 5 contacts of relay RT, conductor M, No. 1 frontcontacts of relay C to ground on conductor 25. Relay SW operates andlocks over its No. 2 front contacts to ground on the No. 1 frontcontacts ofrelay C. When relay A operates at the termination of thefirst pulse, the short circuit around the lower winding of relay P2 isremoved and said relay operates in series with relay Pi over a circuitpath which traces from ground on the No. 2 contacts of relay C, lowerwinding of relay P2, No. 1 contacts of relay Pl, No. 2 contacts ofrelayPZi, winding of relay P1 to battery. Hence after the first pulse isterminated, relays Pl, P2 and SW are operated, the latter being looked,as said before, to ground on conductor 2! through the No. 1 contacts ofrelay 0 which, being slow releasing, remains in an operated positionbetween pulses.

On the beginning of the second pulse, relay A releases again andcompletes a circuit path for relay P3 which extends from ground on itsback contacts, No. 3 contacts of relay B, No. 2contacts of relay E,front contacts and upper winding of relay P2, winding of relay P3 tobattery.

Relay P3 operates and releases relay Pi after which a, circuit iscompleted for relay T2 which extends from battery through the upperwinding of relay T2 and its No. 3 normally made contacts, No. 4 frontcontacts of relay SW, No. 2 back contacts of relay Pl, conductor 23, andthence as previously traced to ground on the No. 1 front contacts ofrelay C. Relay T2 operates, locks through both of its windings in seriesthrough its No. 3 front contacts, No. 5 contacts of relay HS, conductor29 to groundon the No. 5 contacts of relay B and opens the lockingcircuit of relay ST which releases but its release results in no otherfunction at this time.

At the termination of second pulse relay A reoperates and relays P2 andP3 release. Hence at the termination of the second pulse, the pulsingrelays Pi, P2 and P3 are normal, relay C is in an operated position dueto its slow-releasing characteristics, while relays SW and T2 arelocked.

At the beginning of the third pulse, the release of relay A again causesthe operation of relay Piahd the short-circuiting of relay P2 but, inthis case, a circuit is completed for relay T3 which extendsfrom-battery through its upper winding and No. 2 normally madecontinuity contacts, No. 1 contacts of relay DC, No. 5 front contacts ofrelay SW, N0. 5 front contacts of relay T2, N0. 2 front contacts ofrelay PI and thence as already traced to ground on the No. 1 frontcontacts of relay C. Relay T3 operates and, through its No. 2 frontcontacts, locks serially on both windings, to previously traced groundon the No. 5 contacts of relay B. At the end of the pulse relay Areoperates and relay P2 operates in series with relay Pl as previouslydescribed. However, since this is the third and last pulse of the tensdigit, there will be a relatively long interval before the transmissionof the first pulse of the units digit, which interval is sufiicient tocause the release of relay C followed by the release of relay SW and therelease of relays PI and P2 the latter two holding to ground over theNo. 2 contacts of relay 0.

It will beobserved that the dialing of the numeral 3 as the tens digitof the called number has resulted in the operation and locking of relaysT2 and T3. If the tens digit numeral had been a 2 instead of a 3, theresult would have been the operation and locking of only relay T2. N0provision has been made in the link for registering any digit other thana 2 or a 3 as a tens digit since the capacity of the omce is assumed tobe limited to twenty lines, each having a numerical designation from 20to 39. However, it is evident that if any other numerical designationswere to be used, or if the capacity of the office were to be increasedto include more than twenty lines, the link circuit could easily bechanged by any one skilled in the art to register therein any otherdigit for the tens digit.

Prior to the dialing of the second or units digit. relay A is operatedwhile relays PI, P2 and P3 are normal. Upon the first interruption ofthe line loop for the series of pulses of the second or units digit,relay A'will release followed by the operation of relays PI and C aspreviously described, while a circuit is now completed for relay CIwhich extends from battery, resistance RS, the winding of said relay,No. 4 normally made'continuity contacts thereof, conductor 25, No. 1back contacts of relay RT, conductor 26, No. 4 contacts of relay T2, N0.1 contacts of relay SW to ground on the No. 1 front contacts of re layC. Relay Ci operates in this circuit and looks over its No. 4 frontcontacts, No. contacts of relay HS to ground on conductor 20. A circuitis now completed for relay CX, which extends from battery, resistanceCR, through the winding of said relay, No. 3 normally made continuitycontacts of said relay, No. 5 contacts of relay CI, to ground on the No.5 contacts of relay B. Relay CX operates and locks to operating groundover its No. 3 front contacts and, at its No. 1 contacts, opens thecircuit of relay LS! causing it to release and, in turn, release relayLCI which disconnects the translator and alternating current receiverfrom the link, thus causing them to be available for service with otherlinks.

A circuit is also closed for relay I which extends from battery throughits upper winding and No. 5 normally made continuity contacts, No. 1contacts of relay III, No. 3 back contacts of relay II, No. 4 backcontacts of relay V, No. 3 back contacts of relay IV, conductor 21, No.5 back contacts of relay SW, No. 5 front contacts of relay T2, N0. 2front contacts of relay PI and thence as traced to ground on the No. 1front contacts of relay C. Relay I operates and looks with both of itswindings in series through its No. 5 operated contacts, serially throughthe No. 4 continuity contacts of relay II, No. 5 continuity contacts ofrelay III, No. 4 continuity contacts of relay IV, No. 6 continuitycontacts of relay V, conductor 28, No. 5 contacts of relay HS to groundon conductor 28. Upon the termination of the pulse, relay A reoperatesand relay P2 is operated serially with relay Pl.

On the second pulse, relay A releases and, in consequence, relay P3operates in series with relay P2 while relay Pl releases as previouslydescribed. A circuit is now completed for relay II extending frombattery through its upper winding, No. 4 contacts of relay I, conductor29, No. 4 back contacts of relay SW, No. 2 back contacts of relay PI -toground as previously traced to the No. 2 front contacts of relay C.Relay II operates and then locks serially through both of its windingsand No. 4 front contacts to a previously traced ground through thecontinuity contacts of relays III, IV and V. On the break of its own No.4 continuity contacts, relay II releases relay I which thereby restoresto normal.

At the termination of the second Pulse, relay A reoperates and relays P2and P3 release as previously described.

At the beginning of the third pulse, relay Pl reoperates and a circuitis completed for relay III which extends from battery through its upperwinding, No. 3 front contacts of relay II, No. 4 contacts of relay V,No. 3 contacts of relay IV, conductor 21, No. 5 back contacts of relaySW, N0. 5 front contacts of relay T2, N0. 2 front contacts of relay Plconductor 23 to ground as previously traced. Relay III operates on itsupper winding, locks serially with its lower winding and No. 5 frontcontacts to a previously traced ground through the N0. 4 and No. 5continuity contacts of relays IV and V, respectively, while, upon thebreak of its own No. 5 continuity contacts, it releases relay II whichthereby restores to normal. On the fourth pulse, relay Pl will be in anonoperated position and, therefore, a circuit will be closed for relayIV which extends from battery through its upper winding, No. 4 contactsof relay III, conductor 29, No. 4 back contacts of relay SW, No. 2 backcontacts of relay Pl to ground as previously traced. Relay IV operateson its upper winding and then locks serially with pan its lower windingand No. 4 front contacts, through the No. 5 continuity contacts of relayV to ground as previously traced. Upon the break of its No. 4 continuitycontacts, relay III releases and restores to normal.

On the fifth pulse, relay Pl will be operated and a circuit will beclosed for relay V which extends from battery through its upper winding,No. 3 front contacts of relay IV, conductor 21, No. 5 back contacts ofrelay SW, No. 5 front contacts of relay T2, N0. 2 front contacts ofrelay Pl to ground. Relay V operates on its upper winding and locksserially with its lower winding through the No. 3 contacts of relay I,its own No. 5 front contacts to ground as previously traced to the No. 1front contacts of relay C. When it breaks its own No. 5 continuitycontacts it releases relay IV which thereby restores to normal.

On the sixth pulse, relay Pl will be in a nonoperated position whereupona circuit will be completed for relay VI which extends from batterythrough its upper Winding and No. 5 continuity contacts, No. 1 contactsof relay V, conductor 29, No. 4 back contacts of relay SW, No. 2 backcontacts of relay Pl to ground. Relay VI operates on its upper windingand locks serially through its lower winding and No. 5 front contacts toground as previously traced on conductor 28. Relay V, however, willremain locked since its own locking circuit is independent of theoperated condition of relay VI.

On the seventh pulse, relay Pl will be in an operated position whereuponthe previously traced circuit for relay I will be established and relayI will operate in said circuit, locking thereafter serially through itslower winding and No. 5 contacts and through the previously identifiedcontacts of relays II, III and IV, the No. 7 contacts of relay VI toground on conductor 28. Relay V is released upon the operation of relayI.

On the eighth pulse, relay PI will be unoperated and a previously tracedcircuit for relay II will be established, which relay, upon operating,locks serially through its lower winding and No. 4 front contacts,serially through the previously designated continuity contacts of relaysIII, IV and V to ground on conductor 28. Upon the operation of relay II,the locking circuit of relay I is opened at the No. 4 continuitycontacts of relay II and relay I thereby restores to normal. Relay VIremains locked to ground on conductor 28.

On the ninth pulse, relay PI will be operated and a previously tracedcircuit for relay III is established causing said relay to operate onits upper winding and then look serially through its lower winding andNo. 5 contacts, No. 4 continuity contacts of relay IV, No. 5 contacts ofrelay V to ground on conductor 28. Upon the operation of relay III,relay II restores. Relay VI remains locked to ground on conductor 28.

On the last or zero pulse (which will not be dialed by the subscribersince it has been assumed that the units digit will be the digit 9)relay Pl will be normal and a previously traced circuit will beestablished for relay IV which will operate thereover on its upperwinding and then look serially through its lower winding and No. 4continuity contacts, No. 5 continuity contacts of relay V, to ground onconductor 28. Relay VI is still locked to ground on conductor 28.

Thus the pulses of the second digit are registered in the relays I--VIof Fig. 6, the relay or relays operated depending upon the number ofpulses transmitted. The relationship between the number of pulses andthe relays operated is shown in the following table:

Relay Pulses operated It has been assumed that the called subscribersnumber is 39 and, therefore, in respect to the units digit, relays IIIand VI will have been operated.

At the end of the last pulse of the second digit with relay Areoperated, relay C will release and a circuit is then closed for relayDC which extends from battery through its lower winding and No.continuitycontacts, No. 2 contacts of relay C l, No. 1 back contacts ofrelay C to ground on conductor 2!. Relay DC operates on its lowerwinding and locks in series with its upper winding and No. 5 frontcontacts to ground as previously traced on conductor 28. Relay DC, uponoperating, completes a path for relay SW extending from battery throughits upper and lower windings, No. 2 front contacts of relay DC to groundon conductor 28. Relay DC also connects battery through the lowerWinding of relay BY to a conductor which extends to an armature of thehold magnet of the vertical associated with the called line which, inthis case, is hold magnet Ihis path is traced as follows: Batterythrough the lower winding of relay BY, No. 4 ccntinuitycontacts of saidrelay, No. 1 front contacts of relay Cl, No. 4 contacts of relay DC, No.1 front contacts of relay T3, conductor 35, No. 4 front contacts ofrelay VI, conductor 3|, No. 6 contacts of relay DC, conductor 32, No. 6contacts of relay III, conductor 33, lower armature and contact of holdmagnet H539 to the winding of relay 0939. The object of this circuit isto test for the idle or busy condition of the line. Should the line bebusy, hold magnet H039 will be operated, whereupon it will apply groundto conductor 33through its lower front contacts and cause thereby theoperation of relay BY which then looks through its No. 4 front contactsserially through its upper winding, No. 5 contacts of relay HS to groundon conductor 2t). Relay BY applies ground through its No. 1 contacts toconductor 34 extending to the power, tone and alarm circuit Ilil wherebycircuits are closed therein to apply 'a busy tone source to conductor35. This conductor extends over the No. 2 contacts of relay BY, to oneside of condenser Ctthrough which the tone current passes overthe N0. 2back contacts of relay HS, conductor LT over the calling loop previouslytraced to conductor LR, No. 3 back contacts of relay HS, upper windingof relay A to ground. The busy tone thus furnished the callingsubscriber indicates to him that the line is busy, whereupon he restoresthe telephone instrument upon the cradle and thereby opens the circuitof relay A, the release of which initiates the restoration of theapparatus as described hereinafter.

Assuming, however, that the called line is not busy, then hold magnetH039 will be normal tacts of relay El-.

and relay BY will not operate. In this case, a. circuit is closed forrelay LKI of the link in the call allotter, which circuit extends frombattery through the winding of said relay, conductor 36, No. 3 contactsof relay BY, No. 3 contacts of relay SW, No. 3 contacts of relay Cl,conductor 31 to ground on the No, 11 con- Relay LKI operates, completesa circuit for relay Bl in the call allotter, which circuit extends frombattery through the winding of relay Bl, conductor 38, No. 5 contacts ofrelay LKI, conductor 39, No. 2 contacts of relay Cl, No. 1 back contactsof relay C to ground on conductor 2i, and opens the serial locking pathof all relays Ll which, should any of them operate in response to theinitiation of a call during the time that a link is setting up the..terminating end of a connection, the same will be prevented fromlooking at the time relays El and E2 operate in the manner previouslydescribed. The failure of relay Ll to lock will then prevent ground frombeing applied to conductor H over'the contacts of relay MS. In thismanner, a line which calls during the setting up of a connection will beprevented from interfering and, of course, will also be denied serviceuntil the previous connection has been set up. Relay LKI also completesa circuit for relay E of the call allotter which traces from batterythrough its winding, conductor 9, No. 1 front contacts of relay LKl,conductor 31, to round on the No. 11 contacts of relay El. Relay E nowoperates relays El, E2 and MS as previously described and, when thelatter relay operates, a circuit is completed for select magnet 8 whichextends from battery through the winding of said magnet, conductor to,No. 6

contacts of relay LKl, conductor M, No. 1 contacts ofrelay Bl, conductorH, No. 3 contacts of relay MS, conductor H3, to ground on the No. 3contacts of relay LKl. Select magnet 8 operates and pre-selects thehorizontal cross-. points controlled by it and completes a circuit fromground through the contacts of said magnet, conductor l8, windings of Sand SI relays in parallel to battery, causing said relays to operate.The operation of relay S connects ground through its No. 2 contacts,conductor 42, the No. 4 contacts of relay LKI, conductor 43 to thecommon terminal of resistance RS and the Winding of relay Cl causing therelease of the latter. Upon the release of relay Cl, ground is appliedto conductor 33 which, as previously traced, is connected to the windingof relay C839 of the called line til. The path is as follows: Ground onthe No. 1 back contacts of relay Cl, No. 4 contacts of relay DC, No. 1front contacts of relay T3, conductor 39, No. 4 front contacts of relayVI, conductor 3!, No. 6 contacts of relay DC, conductor 32, No. 6contacts of relay III, conductor 33 and thence as traced to the windingof relay C039 to battery. Relay case operates and completes an obviouscircuit for hold magnet H939 which operates to close crosspo-int 2. Theoperation of the hold magnet H839 disconnects operating ground for relayCGBB, but this relay now holds over the No. 4 contacts of crosspoint 2,conductor S, No. 3 back contacts of relay E, No. '7 contacts of relay B,front contacts of relay A (which is being held over the calling lineloop from station A) to ground on conductor Si as previously tracedthereto. Operated cross points I and 2 effect the connection between thecalling line A and the called line B;. Ground "on conductor S2 appliedthereto by the closure of the No. 3 contacts of crosspoint 2 completes acircuit for relay SP, which circuit may be traced from ground on saidconductor, No. 2 front contacts of relay T2, N0. 5 contacts of relay BY,winding of relay SP to battery. Relay SP operates and connects ringingcurrent applied to conductor 4'1 within the bracket line 13 from thepower circuit Ht, through the No. 3 contacts of relay RTR. and lowerwinding thereof, No. 3 front contacts of relay SP, conductor d8, No. 5contact of crosspoint 2, ring conductor RI of the called line, over theloop of station B, tip conductor Tl of the called line, No. 6 contactsof crosspoint 2, conductor 39, No. 2 front contacts of relay SP,conductor 59 within the bracket line [3 to ground connected thereto inthe power circuit Hi]. Ringing current is thus applied to the calledsubscribers line and an audible ringing tone is provided for the callingsubscriber A over a circuit which extends from one side of ringing tonecircuit (not shown) in the Power, etc., circuit H0, conductor ill withinbracket line it, No. 5 contacts of relay SP, condenser C8, condenser C2,and thence as traced over the calling loop to ground through the upperwinding of relay A. The calling subscriber thus hears the ringing tone.When the call is answered, relay RTR will operate and lock over itsupper winding and No. 2 contacts to ground on the No. 4 front contactsof relay SP, and further completes a circuit for relay HS which extendsfrom battery through its winding, conductor 5|, contacts I and 2 ofcrosspoint 2, conductor 52, No. 1 contacts of relay RTR to ground onconductor 2!. Relay HS operates and, by opening its No. 5 contacts,disconnects the ground which holds relays SW, T2, T3, DC and theregister relays III and VI. The release of relay T2 releases relay SPwhich, in turn, releases relay RTR, the former relay connecting thesupervisory relay E to the called line. The circuit of relay E is asfollows: Battery through its lower winding, conductor 53, No. 7 backcontacts of relay LCI, conductor 5 No. 3 back contacts of relay SP,conductor 18 thence as previously traced over the called loop back toconductor No. 2 back contacts of relay SP, conductor 55, No. 8 backcontacts of relay LCI, conductor 56, upper winding of relay E to ground.

Relay E operates and connects ground on its No. 1

contacts and therefrom to conductor 52 which, over the No. 1 and 2contacts of crosspoint 2, joins the conductor 51 which further extendsto the winding of relay HS, thereby holding said relay operated. Overits No. 1 front contacts, relay HS applies ground to conductor S which,through contact 4 of crosspoint 2, extends to the winding of the cut-offrelay C039 of line B to hold said relay in an operated condition. RelayHS also establishes a circuit from ground on conductor 26 over its No. 4contacts, the No. 2 contacts of relay CX to battery through the No. 2normal contacts and winding of relay CON to battery, whereupon relay CONoperates and locks over its No. 2 contacts and the No. back contacts ofrelay CI to ground on conductor 20.

When the calling line A releases, relay A of the link releases anddisconnects ground on conductor S! from conductor 5! but relay HS holds,as said before, to ground on conductor 52. Relay A also disconnectsground from conductor 5? which holds the cut-off relay C020 operated.thereby causing this relay to release, in turn releasing hold magnetH020 and opening crosspoint I. The calling line A is now disconnectedfrom the link. Hence if the calling station should restore first, therelease of relay A merely removes one of the grounds which holds relayHS operated, but the latter, holding to ground on conductor 52 appliedthereto by relay E which holds over the called loop, prevents the linkfrom being disconnected from the called line. The link, therefore, isheld until the called line restores in order to prevent the same fromseizing another link and receiving dial tone in consequence thereof.When the called station restores, relay E releases, disconnects groundfrom conductor 52 releasing relay HS. Relay HS, on releasing,disconnects ground from conductor 52 which releases relay C039 in turnreleasing hold magnet H029 and opening crosspoint 2.

In case it is desired to add a third station to the connection for aconference, the called subscriber will replace the receiver on theswitchhook. As a result of this, relay E releases, disconnects groundfrom conductor 52 and thereby causes the release ,of relay HS. Therelease of relay HS closes a circuit extending from ground on conductor20, No. 5 back contacts of relay Cl, No. 1 contacts of relay CON, No. 6contacts of relay HS, to the common terminal of resistance CR and thewinding of relay CX, causin the latter to release. The release of relayCX causes ground to be applied from conductor 20, No. 1 contacts ofrelay OK to conductor 58, thereby causing the reoperation of relay LSland the reconnection of the translator and alternating current receiverto the link. Key tone is now supplied to the calling subscriber asoriginally described and thereafter he will proceed to dial the numberof the third party. When the first digit is dialed, relay TiZ willoperate as described, in turn operating relay SP over a circuit thattraces from battery through the winding of said relay, No. 5 contacts ofrelay BY, No. 2 front contacts of relay T2 to ground on conductor S2 viathe No. 3 contacts of crosspoint 2. Relay SP, in operating, reconnectsthe ringing circuit to the first called station and causes thereby theoperation of the ringer thereat. Now, when the second called station isconnected to the link in the same manner as called station B, the bellsof the two subscribers will ring, and when the second call-ed subscriberanswers, the bell at station B will cease to ring and this furnishes anindication that the second called subscriber has answered. This acts asa signal to the called subscriber at B to answer also. In case thesecond line is busy, relay BY will operate as described when the line istested for a busy condition and this will cause the release of relay SPsince its circuit is controlled through the No. 5 contacts of relay BYin consequence of which the ringer at station B will cease to operateand the calling subscriber will receive a busy tone. The subscriber atstation B will then answer since the cessation of ringing is either dueto the third party answering or to the third party being busy. Relay HSoperates as before described, releasing relay BY and all the registerrelays. It is to be noted that, on a conference connection of the typedescribed, the stations connected to the terminating end, that is,station B, and the second called station, cannot release until allcalled stations disconnect since relay HS, which can be operated fromany station, will hold to the cut-off relay of any one of the calledstations.

Having described the establishment of a cona in consequence of which alink will be connected to the calling station B in the same manner aspreviously described for station A but, in this case, over crosspoint 3,and when relay ST of the link operates, relays LSI and LCI are operatedto connect the alternating current translator and receiver to the link,relays ON and GR therein being operated and tone being to the callingstation in the manner previously described for station A. a

It will be observed that relay GR, in its unoperated condition, normallyapplies ground to the unoperated No. 2 and No. 5 contacts of relay ONwhich, when operated, connects these contacts to conductors l3 and 14which further extend to the ring RI and tip Tl conductors of the callingline. to the operation of relay B while relay ON operates followingreIayAS T. Now inasmuch as the circuit of relay A is completed as soonas crosspoint 3 is closed and relay ON may be operated at the time, thecurrent build-up in relay A will cause a change in the charge oncondensers C2 and 03 over one path completed from one side of condenser02, conductor 54, No. 7 contacts of relay LCI, conductor 13, Nos. 2 and3 contacts of relay ON, to ground on the No. 2 contacts of relay GR; andanother path from one side of condenser 3, conductor 55, No. 8 frontcontacts of relay L'Cl, conductor 14, Nos. 4 and 5 contacts of relay ONto ground on No. 1 contacts of reuntil relay GR operates, which occursafter the operation of relay B and, therefore, after the currentin relayA has reached its steady state.

Upon hearing tone, the calling subscriber at station B depresses a key(not shown) of the de- Vice LG which designates the first digit of thecalled number, thereby plucking two of its set of five reeds. The reedsare set into vibration and produce two alternating currents of specificfrequencies which are now transmitted over a circuit which may be tracedas previously to conductors I3 and 14 at the Nos. 2 and 5 contacts,respectively, of relay ON and, thereafter, to conductors H and 12,respectively, connecting with the secondary winding of transformer 68-.These frequencies are induced into the circuit comprising the primarywinding of said transformer and the high-pass filter 64.

The receiver circuit in Fig. 9 is a conventional disclosure of thereceiver shown in Patent 2,269,022 issued to G. Hecht and A. A. Lundwstrom on Jan. 6, 1942. It comprises the chan-: nel composed oftransformer 68, the high-pass filter 64, the volume limiting device 65,the transformer 66, the adjustablepad 61, five detector amplifiers fA-fEwith relays FA-FE respec- Relay GR operates subsequent tively in each ofthe anode circuits thereof and a suitable filter intermediate the pad 61and each one of the detector amplifiers, each of said filters beingdesigned to pass only the frequency intended for the particular channel.Between the high-pass filter 64 and the volume limiter $5 is bridged theprimary of transformer H2 to the secondary of which is connected theenabler S'il. This enabler is identical in construction to thatcompletely disclosed and described in the above-mentioned patent to G.Hecht and A. A. Lundstrom and is shown only in conventional form exceptfor relay H. The enabler responds to a portion of,the signal pulseswhich pass through the high-pass filter .64 and functions to operatepolarised relay 1'! after a predetere mined interval. Relay 1'! groundsconductor 18 which is connected to the cathode of each of the detectortubes fAjE thereby activating them to respond to the signal energy whichpasses through the volume limiter 65. Since the operation of the enabler89 is completely described in the above-mentioned patent, reference ismade to said patent for a complete description thereof, only so much ofsaid description as is necessary to an understanding of the presentinvention being incorporated herein.

Each detector amplifier tube is preceded by a filter which passes onlythe frequency to which that tube is assigned to respond. It is assumedthat the device LG is capable of producing five different frequencieswhich, for convenience, may be designated AE inclusive and that, inaccordance with the operation of the receiver as described in theabove-mentioned copending application, frequency A will cause theoperation of tube fA, frequency B will cause the operation of tube f3and so on to frequency E which will cause the operation of tube fE. 1

As already mentioned, .each detector amplifier tube has-a relayconnected to the anode terminal thereof, and a front contact ofthisrelay is further connected to the winding of one of the five relaysTA-TE in the translator circuit shown in Fig. 8. Relay FA in the anodecircuit of the first channel which responds to frequency A has its frontcontact connected to the winding of relay TA, while relay FIB of thesecond channel, responding to frequency B, is connected to the windingof relay TB and so on up to and including relay FE in the anode circuitof the fifth channel which responds to frequency E, the front contact ofwhich relay is connected to relay TE. Hence, the operation of anycombination of detector amplifiers fAfE will cause a correspondingoperation of the register relays in the translator of Fig. 8.

The combination of frequencies for each of the digits which may bedialed from the calling station B, the operation of channel andtranslator relays operated thereby is as follows:

When, therefore, the subscriber keys the first digit, which may be a 2or a 3 but which, in the assumed illustration, will be a 2, frequenciesB and D are generated and these frequencies are transmitted over apreviously described loop including a winding of transformer 68 whencethey pass through high-pass filter 54 from the output of which theenergy thereof divides, part of it passing through transformer H2 tooperate the enabler 80 and part of it passing through the volume limiter65, transformer 66, resistance pad 61, the filters preceding the tubes1B and ID to operate said tubes. Since the operation of the receiver hasbeen amply described in the abovementioned patent to G. Hecht and A. A.Lundstrom and to which reference is made for a complete descriptionthereof, it may be stated that a definite time interval is consumed inthe operation of enabler 80, in consequence of which relay 11 operatesto apply ground to conductor 18. Since this conductor is connected tothe cathodes of the various detectors, those detectors will respondthrough whose channels the filters have permitted the passage of thefrequencies in the signal. Hence for the digit 2 for which thefrequencies B and D are produced to cause the response of channels fBand ID, relays FE and FD will be operated and they, in turn, closeobvious circuits whereby relays TB and TD are operated and, uponoperating, lock over conductor Bl under the control of polarized relayTL to ground on the No. 6 contacts of relay ON; relay TL having operatedover a circuit which may be traced from battery, the No. 2 contacts ofrelay TLT, upper winding of relay TL, No. 3 contacts of relay TLT, No. 3contacts of relays TE and TD, No. 3 contacts of relays TB and TC, N0. 3contacts of relay TA, No. 1 contacts of relays BKI, BK3 and KBD,conductor 16 and ground previously traced thereto. Relay TL also has acircuit through its lower winding which traces from ground on the No. 6contacts of relay ON, No. 4 contacts of relay TLT, lower winding ofrelay TL, No. 1 contacts of relay TLT to resistance battery. Now thecurrent flowing through the upper winding of relay TLT is in a directionto cause the armature to engage the contact, while that through thelower winding is in a direction to do the opposite. The strength of thecurrent through the lower winding, however, is not sufiicient by itselfto overcome the eifect of the current flowing through the upper windingso that, when both windings are energized, the armature will engage itscontact and provide locking ground for relays TB and TD as abovedescribed.

It will be noted that the ground which forms a part of the circuit ofthe upper winding of relay TL also keeps condenser C5 short-circuited.However, the operation of any one of the register relays TATE removesthis ground and a charging circuit is established for the condenserthrough the circuit of the upper winding of relay TL. Relay TL continuesto hold for a short interval until the charging current through thecondenser dies down after which. being solely responsive to the currentthrough its lower windrelays TB and TD and during the interval that 75the same are locked to the contacts of relay TL, a circuit is completedin the link to operate relay T2 which is the relay in the link thatregisters the digit 2 as previously described. This circuit is completedfrom ground on conductor 16, No. 1 contacts of relays KBD, BK3 and BK!,No. 3 contacts of relay TA, No. 3 contacts of relay TC, No. 4 contactsof relay TB, No. 6 contacts of relay TD, No. 9 contacts of relay TE, No.2 contacts of relay TB, No. 11 contacts of relay TD, conductor 83, No. 3contacts of relay LCl, conductor 84, No. 2 back contacts of relay RT,conductor 85, upper winding of relay T2 to battery. Relay T2 operatesand then locks as previously described to register the first digit 2. Ifthe first digit of the called number had been a 3 instead of a 2, then,according to the above table, relays TD and TE would have been operatedin consequence of the operation of channel relays FD and FE in whichevent, in addition to closing a circuit for relay T2, a circuit willalso be closed for relay T3 and this circuit may be traced from groundon conductor '16, No. 1 contacts of relays KBD, BK3 and BKI, No. 3contacts of relay TA, No. 3 contacts of relay TC, No. 3 contacts ofrelay TB, No. 4 contacts of relay TD, No. 6 contacts of relay TE, N0. 1contacts of relay TD, No. 2 contacts of relay TE, conductor 86, No. 1contacts of relay LCl, conductor 81, No. 3 back contacts of relay RT,conductor 83, No. 2 normally made continuity contacts of relay T3, upperwinding of said relay T3 to battery. Relay T3 operates and then looks aspreviously described to register the digit 3.

Simultaneously with the operation of the register relays TB and TD inresponse to the keying of the tens digit 2, or with the operation ofrelays TD and TE for the digit 3, a circuit is completed for relay RA.For either digit, the ground on conductor 15 may be traced to the commonconductor joining the No. 6 and No. 9 contacts of relay TE. These pathsare through a network of contacts which extends over the contacts ofrelays TATE in order to insure that exactly two of these relays areoperated before grounding any of the link registers. From the commonterminal of this network at the Nos. 6 and 9 contacts of relay TE, thecircuit for relay RA may further be traced through either No. 1 contactsof relay TE or No. 1 contacts of relay TB, No. 10 contacts of relay TD,No. 5 back contacts of relay RAI, No. 1 normally made continuitycontacts of relay RA, No. 1 contacts of relay RR, winding of relay RA tobattery. Relay RA operates and, by the closure of its No. 1 frontcontacts, applies ground on conductor 1'6 to one terminal of the windingof the relay RAI, the other terminal being grounded over the No. l backcontacts of said relay by the afore-traced ground for operating relayRA. Relay RA, in operating. opens the tone circuit at its No. 2 contactsthereby removing dial or key tone from the line.

7 removed from the battery side of the winding of relay RAI causing saidrelay to operate by the circuit completed to an afore-traced ground onthe No. 1 front contacts of relay RA. Relay RAI, in operating, closes acircuit for relay RT the path of which extends from groundon the No. 1contacts of relay RAl, conductor 89, No. 2 contacts of relay LCI,conductor 9|, winding of .relay RT to battery. Relay RT operates, locks

